Treating slurries

ABSTRACT

This invention relates to a composition for treating inorganic slurries and to a method of treating inorganic slurries with the aforesaid composition so as to maintain the slurries in a substantially homogeneous phase. The composition comprises a THP +  salt and a dispersant selected from the group consisting of: (i) phosphonated compound containing at least one tertiary nitrogen atom; (ii) phosphonated oligomers of unsaturated acids; (iii) homopolymers of unsaturated acids; and (iv) Polyphosphates The THP +  salt is preferably THPS

This invention relates to a composition for treating inorganic slurriesand to a method of treating inorganic slurries with the aforesaidcomposition so as to maintain the slurries in a substantiallyhomogeneous phase.

The present invention will be described herein with particular referenceto calcium carbonate-based slurries, especially those used inpaper-making processes, although it is not to be construed as beinglimited thereto.

Most inorganic slurries contain about 70% to 80% by weight of solids.Many inorganic slurries (particularly those based on calcium carbonate)are known to be susceptible to bacterial contamination and it has beenthe practice to add one or more biocidally-active materials to theslurries in order to minimise such contamination.

Phosphorus-containing compounds, in particulartetrakis(hydroxyorgano)phosphonium salts (THP⁺ salts) are known to beeffective biocides. Experimental work carried out by the applicants hasshown, for example, that the addition of a solution oftetrakis(hydroxymethyl)phosphonium sulphate (THPS) to a calciumcarbonate-based slurry can give rise to a reduction in bacterial countof 10⁴ in 2 hours.

However, it is also known that addition of THPS alone to a slurryresults in instantaneous heterogeneous thickening and aggregation of theslurry.

The applicants have found that the use of a composition comprising aTHP⁺ salt and a dispersant will provide continuing preservation againstbacterial contamination, while at the same time maintaining the slurryin a substantially homogeneous phase.

Accordingly, in a first aspect, the present invention provides acomposition for treating an inorganic slurry, the compositioncomprising:

-   (a) a tetrakis(hydroxyorgano)phosphonium salt (hereinafter THP⁺    salt); and-   (b) a dispersant selected from the group consisting of:    -   (i) phosphonated compounds containing at least one tertiary        nitrogen atom;    -   (ii) phosphonated oligomers of unsaturated acids;    -   (iii) homopolymers of unsaturated acids;-   and (iv) polyphosphates.

In accordance with the present invention, the THP⁺ salt is preferablytetrakis(hydroxymethyl)phosphonium sulphate.

Alternatively, the THP⁺ salt may be tetrakis(hydroxymethyl)phosphoniumchloride, phosphate, nitrate or oxalate.

A preferred example of a dispersant of the type (b)(i) is a compoundhaving one tertiary nitrogen atom, such as a sodium salt ofnitrilo-tris(methylene phosphate), particularly the tetra-sodium salt.

Preferred examples of dispersants of the type (b) (ii) include thoseoligomers having the general H(CH₂OM.CH₂OM).PO₃M₃, wherein M is acationic species such that the oligomer is soluble in water and n is anumber greater than 1.

Other suitable oligomers are disclosed in the applicant's EuropeanPatent Specification 0 491 391.

A preferred example of a dispersant of the type (b)(iii) is ahomopolymer of acrylic acid, especially a homopolymer having a molecularweight in the range 2000 to 5000.

Preferred examples of dispersants of the type b(iv) include sodiumtripolyphosphate.

In a second aspect, the present invention provides a method of treatingan inorganic slurry to maintain the slurry in a substantiallyhomogeneous phase, the method comprising the addition to the slurry ofan effective amount of a composition according to the first aspect ofthe present invention.

The inorganic slurry may, for example, comprise a calciumcarbonate-based slurry.

Alternatively, the inorganic slurry may comprise a pigment slurry, aclay slurry or a cement slurry.

Preferably, the ratio of THP⁺ salt to dispersant in the composition isabout 2:1 (as active ingredients).

Suitably, the composition may be added to the slurry in an amount in therange 10 ppm to 1000 ppm (by weight of the slurry), for example about750 ppm (by weight of the slurry).

The present invention will be illustrated by way of the followingexamples.

In the examples, a 75% calcium carbonate slurry (commercially known asSetacarb) was treated with:

EXAMPLE 1 THP⁺ Salt Alone EXAMPLE 2 THP⁺ Salt and Dispersant of Type(b)(i). EXAMPLE 3 THP⁺ Salt and Dispersant of Type (b)(ii).

The amounts of each additive used, and the results, are given in theTABLE below. TABLE Example THP⁺ salt Dispersant No. (ppm) (ppm) Result 1(a) THPS (b) (nil) Instant heterogeneous 750 ppm thickening 2 (a) THPSb(i) No thickening 750 ppm 375 ppm 3 (a) THPS b(ii) No thickening 750ppm 375 ppm

Notes to TABLE

-   -   (a) An aqueous solution of tetrakis(hydroxymethyl)phosphonium        sulphate (75% a.i.), available as TOLCIDE®-PS75.    -   (b) (i) An aqueous solution of the tetra sodium salt of        nitrilo-tris(methylene phosphonic acid), available as BRIQUEST®        301-32S.    -   (b)(ii) A homopolymer of polyacrylic acid, having a molecular        weight in the range 2000-5000 and available as BEVALOID®211.

1-19. (canceled)
 20. A method for treating an inorganic slurry tomaintain the slurry in a substantially homogeneous phase and to preservethe slurry against bacterial contamination, which comprises the additionto the slurry of an effective amount of a composition comprising: (a) atetrakis(hydroxyorgano)phosphonium salt (herein THP⁺ salt) selected fromtetrakis(hydroxymethyl)phosphonium sulphate,tetrakis(hydroxymethyl)phosphonium chloride,tetrakis(hydroxymethyl)phosphonium phosphate,tetrakis(hydroxymethyl)phosphonium nitrate andtetrakis(hydroxymethyl)phosphonium oxalate; and (b) a dispersantselected from the group consisting of: (i) phosphonated compoundscontaining at least one tertiary nitrogen atom; and (ii) homopolymers ofunsaturated acids.
 21. A method according to claim 20, in which the THP⁺salt is tetrakis(hydroxymethyl)phosphonium sulphate.
 22. A methodaccording to claim 20, in which the THP⁺ salt istetrakis(hydroxymethyl)phosphonium chloride, phosphate, nitrate oroxalate.
 23. A method according to claim 20, in which the dispersant(b(i)) is a phosphonated compound containing one tertiary nitrogen atom.24. A method according to claim 4, in which the dispersant (b(i)) is asodium salt of nitrilo-tris(methylene phosphonate).
 25. A methodaccording to claim 5, in which the salt is the tetra-sodium salt.
 26. Amethod according to claim 20, in which the dispersant (b(ii)) is ahomopolymer of acrylic acid.
 27. A method according to claim 26, inwhich the homopolymer has a molecular weight in the range 2000 to 5000.28. A method according to claim 20, in which the ratio of THP⁺ salt todispersant in the composition is about 2:1 (as active ingredients). 29.A method according to claim 20, in which the composition is added to theslurry in an amount in the range 10 ppm to 1000 ppm (by weight of theslurry).
 30. A method according to claim 20, in which the composition isadded to the slurry in an amount of about 750 ppm (by weight of theslurry).
 31. A method, according to claim 20, in which the slurrycomprises a calcium carbonate-based slurry.
 32. A method according toclaim 20, in which the slurry comprises a pigment slurry, a clay slurryor a cement slurry.
 33. A composition for treating an inorganic slurry,the composition comprising: (a) tetrakis(hydroxyorgano)phosphonium salt(herein THP⁺ salt) selected from tetrakis(hydroxymethyl)phosphoniumsulphate, tetrakis(hydroxymethyl)phosphonium chloride,tetrakis(hydroxymethyl)phosphonium phosphate,tetrakis(hydroxymethyl)phosphonium nitrate andtetrakis(hydroxymethyl)phosphonium oxalate; and (b) a dispersant whichis the tetra sodium salt of nitrilo-tris (methylene phosphonate).
 34. Acomposition according to claim 33, wherein the THP⁺ salt istetrakis(hydroxymethyl)phosphonium sulphate.
 35. A method of treating aninorganic slurry to maintain the slurry in a substantially homogeneousphase and to preserve the slurry against bacterial contamination,comprising the addition to the slurry of an effective amount of acomposition according to claim
 33. 36. A composition for treating aninorganic slurry, the composition comprising: (a) atetrakis(hydroxymethyl)phosphonium salt (herein THP⁺ salt) selected fromtetrakis(hydroxymethyl)phosphonium sulphate, tetrakis(hydroxymethyl)phosphonium chloride, tetrakis(hydroxymethyl)phosphoniumphosphate, tetrakis(hydroxymethyl)phosphonium nitrate andtetrakis(hydroxymethyl)phosphonium oxalate; and (b) a dispersant whichis a homopolymer of acrylic acid, the homopolymer having a molecularweight in the range of 2,000 to 5,000.
 37. A composition according toclaim 36, wherein the THP⁺ salt is tetrakis(hydroxymethyl)phosphoniumsulphate.
 38. A method of treating an inorganic slurry to maintain theslurry in a substantially homogeneous phase and to preserve the slurryagainst bacterial contamination, comprising the addition to the slurryof an effective amount of a composition according to claim 36.